Atmospheric dust originating from mine tailings and other mining operations is a potentially important human exposure route for arsenic, lead and other toxic elements in the arid Southwest, and will become increasingly important here and elsewhere with predicted regional climate change and population growth. Dust particles emitted from mining operations mobilize trace metals which can then accumulate in soils, natural waters, and vegetation. Human exposure to the dust can occur through inhalation and, especially in the case of children, incidental dust ingestion. This project will use Micro-Orifice Uniform Deposit Impactor samplers to collect atmospheric aerosols in ten size fractions (0.056 microM to 18 microM aerodynamic diameter), downwind of two Superfund sites - contaminated mine tailings at Hayden-Winkleman and Iron King, AZ. The separate fractions will yield size-fractionated mass concentration data for toxic metals and metalloids (As, Pb, Cr, Cd, Sb), as well as other physicochemical characteristics. A scanning mobility particle sizer (SMPS) will allow us to count the number of ultrafine particles, which are thought to be most closely linked to adverse health effects. Using these tools, the following Aims will be addressed: 1) assess the role of atmospheric dust in the transport of metals contaminants from mine operations 2) identify contaminant source to assess remediation approaches 3) in collaboration with Project 9 assess role of vegetation cover to reduce dust emission 4) incorporate results into University of Arizona - Dust Regional Atmosphere Model for prediction of dust emissions and human exposures These studies will be performed in collaboration with Region 9 EPA and the State of Arizona Department of Environmental Quality. The results of these studies will be critical additions to the information that these agencies utilize for risk assessment of down-wind exposed populations.